Calculate Delta H for The Following Reaction 2so2

This calculator helps you determine the enthalpy change (ΔH) for the reaction 2SO₂ + O₂ → 2SO₃ using standard enthalpy values. Enthalpy change is a measure of the heat absorbed or released in a chemical reaction.

How to Calculate ΔH

The enthalpy change (ΔH) for a reaction can be calculated using the standard enthalpies of formation (ΔHf) of the products and reactants. The formula is:

ΔH = ΣΔHf(products) - ΣΔHf(reactants)

Where:

ΔHf(products) is the sum of the standard enthalpies of formation of all products
ΔHf(reactants) is the sum of the standard enthalpies of formation of all reactants

For the reaction 2SO₂ + O₂ → 2SO₃:

Reactants: 2SO₂ and O₂
Products: 2SO₃

You'll need the standard enthalpies of formation for each of these species. These values are typically found in thermodynamic tables or chemistry databases.

Formula Used

The calculation follows this exact formula:

ΔH = [2 × ΔHf(SO₃)] - [2 × ΔHf(SO₂) + ΔHf(O₂)]

Where:

ΔHf(SO₃) is the standard enthalpy of formation of sulfur trioxide
ΔHf(SO₂) is the standard enthalpy of formation of sulfur dioxide
ΔHf(O₂) is the standard enthalpy of formation of oxygen gas

The coefficients (2) account for the stoichiometry of the reaction.

Worked Example

Let's calculate ΔH for the reaction using these standard enthalpy values:

ΔHf(SO₃) = -395.7 kJ/mol
ΔHf(SO₂) = -296.8 kJ/mol
ΔHf(O₂) = 0 kJ/mol (by definition)

ΔH = [2 × (-395.7)] - [2 × (-296.8) + 0]

ΔH = [-791.4] - [-593.6]

ΔH = -791.4 + 593.6

ΔH = -197.8 kJ

This means the reaction releases 197.8 kJ of heat per mole of reaction.

Interpreting Results

The ΔH value tells you about the energy changes in the reaction:

Negative ΔH: Exothermic reaction (releases heat)
Positive ΔH: Endothermic reaction (absorbs heat)

For our example (-197.8 kJ), the reaction is exothermic, which is typical for many oxidation reactions.

Note: These calculations assume standard conditions (25°C and 1 atm pressure). Real-world conditions may affect the actual ΔH value.

FAQ

What is standard enthalpy of formation?: The standard enthalpy of formation (ΔHf) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.
Where can I find standard enthalpy values?: Standard enthalpy values can be found in chemistry textbooks, thermodynamic tables, or online databases like the NIST Chemistry WebBook.
What units are used for ΔH?: ΔH is typically measured in kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).
Can ΔH be negative?: Yes, a negative ΔH indicates an exothermic reaction where heat is released to the surroundings.
How does ΔH relate to bond energies?: ΔH is related to bond energies but also accounts for other factors like lattice energy, solvation, and electronic effects.